Re: LL32 Multihoming

> From: "Erik Guttman" <[email protected]>
>
> If an algorithm is run independently, then it is not aware of others
> running the same algorithm.  Since the algorithm prevents assignment
> of the same address to two different interfaces, a host running the
> algorithm independently on two interfaces would end up with two
> distinct addresses.
>
> > The only difference between two interfaces on the same host and two
> > interfaces on different hosts is that in the former case communication
MAY
> > take place internally rather than taking network bandwidth. The
algorithm
> > need only be aware of other interfaces insofar as it may make life
difficult
> > for a host if it has the same LL address on multiple interfaces.
>
> This is a situation which is useful to avoid, as Erik Nordmark pointed
> out.

If the algorithm is truly run independently then there is a possibility that
quite by chance, two interfaces will pick the same IP and unless they are on
the same link, they might both successfully claim it. Whether or not this is
a problem depends on implementation issues (routing, interface
identification etc.) rather than on our spec.

I don't know whether this needs a mention or not.

If the host intentionally links the IP address on two interfaces (the
problem you mention) then the algorithm is certainly not being run
independently.

> > How about adding the following two paragraphs at the end of section 3.4.
> >
> > "In particular ARP packets which appear to claim an address which is
> > assigned to a specific interface, indicate conflict only if they are
> > received on that interface and their hardware address is of some other
> > interface."
> >
> > "If a host has two interfaces on the same network, then claiming and
> > defending on those interfaces must ensure that they end up with
different
> > addresses just as if they were on different hosts."
>
> I am OK with this text, but I believe this goes without saying.

I also believe this goes without saying. However, Stuart seemed to find
"independent" too vague and I hoped this might clarify. Particularly as
there had been a suggestion on this list that consideration of the hardware
addresses of other interfaces might somehow came into the algorithm - which
I would say contravenes independence.

It is best left out unless others here think there is vagueness or ambiguity
which needs clarifying.

Philip